An HVAC system, such as an air conditioning system for a transport vehicle (e.g., a passenger bus, passenger railcar, etc.), may be included on a transport vehicle to condition air of an interior space (e.g., passenger compartment) of the transport vehicle. In some transport vehicles, the transport HVAC system can be installed externally (e.g., on a rooftop of the transport vehicle). The transport HVAC system can include a fresh air intake to input fresh air into the interior space of the transport vehicle. The transport HVAC system can also be configured to return air that is not fresh to the environment.